Process for treating iron



.- ltpera ure of b tw 2850" centlgmd,

Patented Feb. 23, 1926.

UNITED .VLSTAITE PATENT OFFICE-1' wInLmn- J. nmnnnxcns AND ANsonjnAYEs, orv Arms, Iowa rnocnss on TREA ING molt. i

: 1nd Drawing. Original application nla au u t 21, 1922, Serial No. 583,370. *mvidd'ana this applicaa 1 tion filed Angus 6, 1925. Serial no. 48,623.

To all whom it may cancer n11 Be it known that we, WVI'LLIAM J. DIE- n 011s and ANsoN HAYES, each 'a citizen of the United States of. America, and resident 6 of Ames, Story County, Iowa, have invented a new and useful Process for Treating Iron,

of which the following is a specification. The subject matter of this application was originally included in but has been divided from our application filed 'August 21, 1922, Serial Number "583,370. 1

The object of this invention is toprovide a new and improved process for treating white cast iron whereby an/iron is produced practically du licating the properties of commercial ma leable iron, and in a much shorter time than now required in the ordinary malleabili'zing process.

A further object .of this invention is to. shorten the time required for producing -malleable iron. w

These and other ob'ects of the invention will be more clearly escribed in the specification and pointed out in the appended claims. a 1

. Any suitabletype or form of furnace or so-calle-d annealing oven may be employed in carrying outour improved" process, and may be heated'by any of the'well known forms of fuel-such as gas, oil, or powdered T 'coalburned. in connectlon with air; or the heat maybe secured electrically orv by a combination of combustion and electricity, or in any other manner that may be des'red so long as the desired temperatures an "atmospheres are attained. q

. The iron used inthls processis known as.

white cast iron such as is usedin making malleable castings. This whlte cast .iron

- principally in the ram. of .carbid, .oi. iron It is well known that ordinarily in malt aing malleable cafstin s the white iron is -packed with some pac ng mai e ial in sealed J .,:boxes or ots which are loaded [into the ,,;furna ce w ile the,:gfurna'ce is cold and the,

'furnace is ,then gradually raised, to a. .teinmama t that empe agree, which in the ordinary malleabilizing process, al-

though that may be done at times ifdesired.

I diflersprincipally from ordinary gray iron in that-while both conta n carbon the white j cast iron contains the carbon ,wholly or' v composition o' fthe" whjteAron being treated .graycast iron; contains. the;i.carbon, to a I In any caseit is only desired to; maintain greater degreeingthe form of graphite or th'e lugher temperature until the massive graphitic carbon.

the hig'ih) temperature for a] longer eriod ture for approximately sixt" hours, afte which the furnace is gradua ly cooled, 1: whole process requiring seven to nine days of continuous operation. In the making. of malleable castings the iron carbid is changed mainly to iron and temper carbon or. graphite, the resulting iron usually having a lower tensile strength than the white cast iron from which it was made, but it will bend or stretch to an appreciable deis not true (ofthe white'cast lI'OIl.

In carrying out our improved process we use thewhite cast iron just as in the process above described,-but we employ a very different and much shorter process, which may involve higher temperatures at times. By

this process we obtain ,a; product rully as characteristic and practically duplicating all the properties of malleable iron produced by the now common and well known methods, but ina much short er time In carrying out this'process we do not necessarily pack the white iron castings as By omitting'it considerable time is saved.

- When the packing is omitted the white iron castings may be'supported inany suitable mannerinthe furnace to prevent sagging andwarping under the intense heat. 'The "process consists in heating'forany length of time, raising theftemperatureof the white iron castings with convenient rapidity, either rapidly or slowly,"to any point be tween critical temperature off the material (about 740' degrees centigrade and the point of incipient fusion, and ho ding at the chosen higher temperature' for a period of fifteen minutes to five hours, 'orjjmore. The a'ctual'time required will depend upon "the temperature chosen, lower temperatures requiring longer times, and uponthe chemical :"solids'olution." lVe' are satisfied that in most instances it I would avail "little "to hold at than afut'five hours, since 'practica 1y all y of the desirable change wouldhave occurred as time p a11y* i th 'h grees perature employedgis' above" QOUdgreeS cenewmenswear? used ,the time; required to' practical plete the absorption of massive cementite into the solid solution will be verymaterially in..

creased.

The castings may then bore-moved from the furnace and cooled by quenching in any suitable material such as sand, cement, powdered mica or the like; or the may be cooled. -in any suitable'manner. T ese operations may be repeated for any desired number of repetitions, that is to say, the material may be alternately heated to a point above the critical temperature and then cooled-rapid ly to atem erature considerably below the critical. Tile number of repetitions or alternate heating and cbolings, as well as the rates of heating, mav be varied in accordance with the properties desired in the prodnot.-

The final step of the process consists in niaking the final cooling extremely slowlf', preferably at the rate of about five- (e rees centigrade per hour. This 'is the step which insures and characterizes the product as malleable iron, as by the addition of this step a product is obtained duplicating approximately the characteristics and properties of commercial malleable iron, that is having a tensile strength of from 44,000 to 53,000 pounds per square inch or more and an elongation or ability to stretch of ten rcent or more in two inches. The rocess 1s much shorter than that now carried out to obtain commercial malleable iron, the saving in time depending considerably, of course, upon the number ofrepetit-ions of heating and cooling employed in a particular instance.

vby an extremely slow cooling, we obtain a an is, undercooled resultin material of the same properties as that o tained by either one of the methods individually.

\Vhen speaking of the critical temperature of the material, the fact should be borne in mind, which is well known in metal- .lur that the-critical temperature can be b a rapid cooling, an therefore will be ucedy hestingto a tem rsture above the critical and cooling fai y rapifiy; so that in thereafter heating to the cnti temperature,it is obvious'that a lower actual tem rature will be involved.

ification and that is u v with this fact in" mind and shoal beso eonqgrued.

Tbs. th g' lu h ch racterizes our present invention and process, and differentiates from the process disclosed and claimed in our parent application above referred to, is that in the present instance .the cooling, after each heating to a point above the critical temperature, 15 continued until comparatively low tem ratures are reached. This may be accomplis ed, if desired, by removing from the furnace and quenching in some suitable material, which obviously results in further saving of time, but requires more handling of the material.

As an example of our experiments in conducting this process, we heated bars of white cast iron to about 1000 degrees centigrade for two hours, cooled in sand to room temperature, reheated to 800 degrees centigrade for six hours, and then cooled very slowly, at the rate 'of about five degrees centigrade per hour. The resultant product showed a tensile strength of 48,000 pounds per square.

inch, with an elongation of fourteen percent in two inches.

Likewise by way of illustration, bars of white cast iron were heated to 850 degrees centigrade and cooled to room-temperature by quenching in sand, for variousinumber's of repetitions, the final cooling being at a slow rate of about four de per hour. Bars so 'heate thirteen times gave a tensile strengeh square inch with H en @per cent elongation in. tw o inches and bars so heated seventeen times showed a tensile strength of $9,100

pounds per square inch and an elongation of sixteen rcent in two inches.

es centigrade j of 50,000 pounds per This indicates that a product having the characteristics of commercial malleable iron may be secured by this process in a much shorter time than by the resent that the pro rties may be varied somewhat by the num r of successive beatings and coolings to which the material is subjected, and also by the rates of'cooling employed.

We claimas our invention- 1. The rocess for the heat treatment of m white cast iron which consists in (1) subjecting of the casting to a temperature above the critical temperature 0 ing to a temperature considerabl original critical temperature; (Bl reheating the casting to a suflicient temperature to the material; (2) cooling the caste allow structural and chemical changes to progress; and (4) cooling the casting at process, and

below the v y slow rate-of about five degrees.

for the heat treatment of tem return above the critical temperature structural and chemical changes to progress; (4) cooling the casting to a point where structural and chemical changes cease; (5) alternate repetition of steps (3) and (4); and (6) a final heating to a point where structural and chemical changes can progross, followed by an extremely'slow cooling, at the rate ofabout five degrees centigrade per hour. 7

3. The rocess for the heat treatment of castings rom white cast iron which consists in (1) subjecting of the casting to a temperature considerably above the critical temperature of the material for a period of from fifteen minutes to five hours, or more, until the iron carbid present is Practically all absorbed in the solid solution, or in other words until in irons of commercial composition the combined carbon is reduced to substantiallynine-tenths of one percent; (2) cooling of the casting by quenching; (3) a final heating to a point above the critical temperature; followed by (4) an* extremely slow cooling, at the rate of about five degrees centigrade per hour.

4. The grocess for the heat treatment of castings om white cast iron which consists in (1) subjecting of the casting to a.

. temperature considerably above the critical temperature of the material for a period of rocess for the heat treatment of castings rom white cast iron which consists in (1) subjecting of the casting to a temperature considerablyabove the critical 1 temperature of the material for a period of from fifteen minutes to five hours, or more (2) cooling the casting by quenching; (3) repetition of the above named steps alternately; and a final step consisting in (4) an extremely slow cooling, at the rate of about five degrees centigrade per hour.

Signed at Des Moines, in the county of Polk and State of Iowa, this 18th day of June, 1925.

WILLIAM J. DIEDERICHS. ANSON HAYES. 

